blkio: fix for modular blk-cgroup build

After merging the block tree, 20100414's linux-next build (x86_64
allmodconfig) failed like this:

ERROR: "get_gendisk" [block/blk-cgroup.ko] undefined!
ERROR: "sched_clock" [block/blk-cgroup.ko] undefined!

This happens because the two symbols aren't exported and hence not available
when blk-cgroup code is built as a module. I've tried to stay consistent with
the use of EXPORT_SYMBOL or EXPORT_SYMBOL_GPL with the other symbols in the
respective files.

Signed-off-by: Divyesh Shah <dpshah@google.com>
Acked-by: Gui Jianfeng <guijianfeng@cn.fujitsu.cn>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index 5b49613..906a0f7 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -41,6 +41,7 @@
 	return (unsigned long long)(jiffies - INITIAL_JIFFIES)
 					* (NSEC_PER_SEC / HZ);
 }
+EXPORT_SYMBOL_GPL(sched_clock);
 
 static __read_mostly int sched_clock_running;